Week 1: Intro to a Delicious Summer

June 7th, 2013

My first week in Bloomington has been great! I was sort of dreading my return to the Midwest, but after being in the desert for a week I appreciate the moisture and lack of dust. Not to mention, the weather has been in the 70s all week! Also, the people I’ve met in the lab are extremely nice, including Dr. Gilbert and Dr. Pavlis. At the end of the first day in the lab, Dr. Pavlis invited Dr. Gilbert, Bradley, and me over for dinner, and we had a great time just chatting and getting to know each other. As for the town, Bloomington is your typical college town but with some interesting novelties. There is an entire street lined with every type of ethnic restaurant you can imagine: Indian, Southeast Asian, Turkish, Tibetan, Mediterranean, and the list goes on. Tonight, Bradley and I tried the Tibetan restaurant and it was amazing… my favorite thing about Bloomington so far. Although housing in Indiana is pretty cheap, I’ll definitely be making up for it by eating unnecessary amounts of good food.

Now on to my research project, the reason why I’m ACTUALLY here. I feel like I have really learned a lot in this first week alone. Being completely new to unix, I felt miles behind at the beginning of the week, but after stumbling around for a while I’m finally feeling somewhat comfortable with the basics of the syntax and the structure of Dr. Pavlis’ database. There are three main programs that I’ve spent this week learning to use. Essentially, they allow us to quickly compare the time series traces for each earthquake between all of the OIINK stations. We can then average or “stack” the traces for each event, resulting in a single trace from which we can determine the first P-wave arrival. This data is then used to create a map of residual velocities within the crust which will eventually be combined with other earthquake events to create a 3D velocity map. Although this is technically data that will be used for Bradley’s P-wave tomography project, we both spent most of the week processing data for the 2012 OIINK stations in the way. The idea is that it is a way for me to practice seeing what a “good” broadband seismic trace looks like for when I begin my own data analysis.

The most interesting thing that I’ve experienced this week was during a data analysis session. For a couple of the earthquake events, about half of the stations didn’t show any signal at all; the rest looked completely normal. It was as if half of the stations had been shut off! I was trying to figure out what I had done wrong when Dr. Pavlis walked up behind me and shouted, “That’s a perfect example of the P-wave shadow zone!”. From about 104 – 143 degrees, P-waves are shadowed by the earth’s core due to diffraction. It turns out that the earthquake event I was looking at was exactly at the edge of the 143 degree distance from the stations. I had learned about this phenomenon in my geology class but to actually see it in my data was really cool!

An illustration of the P-wave shadow zone:

What I found in the data:
The y axis shows the station number for both graphs. Starting at station 17, shadowing occurs. This corresponds to just under 145 degrees!